Hard-film-coated drill

Abstract

In a hard-film-coated drill having a cemented carbide drill body coated with a hard film, the drill body is provided with a smooth region at a boundary between a flank surface and a rake surface. The surface hardness of the hard film is within 2000 to 2500 HV in Vickers hardness. A radius r1 (μm) of curvature of the first ridgeline L 1 where the smooth region and the flank surface intersect is represented by r1=0.45×D+a1 (10≤a1≤25), where D is the diameter (mm) of the body. A radius r2 (μm) of curvature the second ridgeline L 2 where the flank surface and a margin intersect is represented by r2=0.65×D+a2 (39≤a2≤67). A thickness t1 (μm) of the hard film is represented by t1=0.8×ln(D)+a3 (0.7≤a3≤3.0).

What is claimed is: 
     
       1. A hard-film-coated drill having a drill body with a surface coated with a hard film, the drill body being made of a cemented carbide and having two or more cutting edges, a flank surface, a rake surface, and a margin,
 wherein the drill body is provided with a chamfered surface adjacent to the flank surface and the rake surface, 
 a surface hardness of the hard film is within a range of 2000 to 2500 HV in Vickers hardness, 
 a first ridgeline where the chamfered surface and the flank surface intersect and a second ridgeline where the flank surface and the margin intersect are formed in a round shape in cross section, 
 a radius r 1  (in μm) of curvature of the round shape of the first ridgeline is within a range represented by a formula r 1 =0.45×D+a 1  (10≤a 1 ≤25), where D is a diameter (in mm) of the drill body and a 1  is a constant (in μm) to keep r 1  within an upper limit and a lower limit, and 
 a radius r 2  (in μm) of curvature of the round shape of the second ridgeline is within a range represented by a formula r 2 =0.65×D+a 2  (39≤a 2 ≤67), where a 2  is a constant (in μm) to keep r 2  within an upper limit and a lower limit, 
 wherein the hard film includes a first layer formed of a first hard film containing a nitride that includes Al and Ti, a second layer formed by alternately stacking second and third hard films having different compositions, and a third layer formed of a fourth hard film containing a nitride that includes Ti and Si, and the first to third layers are stacked in this order from a drill body side, and 
 wherein the second hard film contains a nitride that includes Ti, Al and Si, and the third hard film contains a nitride that includes Ti, Al, Cr and Si. 
 
     
     
       2. The hard-film-coated drill according to  claim 1 , wherein a thickness t 1  (in μm) of the hard film is within a range represented by a formula t 1 =0.8×In(D)+a 3  (0.7≤a 3 ≤3.0), where a 3  is a constant (in μm) to keep t 1  within an upper limit and a lower limit. 
     
     
       3. The hard-film-coated drill according to  claim 2 , wherein the radius r 1  of curvature of the round shape of the first ridgeline is within a range of 15 to 35 μm. 
     
     
       4. The hard-film-coated drill according to  claim 1 , wherein the radius r 1  of curvature of the round shape of the first ridgeline is within a range of 15 to 35 μm.